1. Field of the Invention
The present invention relates to bonding techniques and more particularly to a selective bonding interconnection mask sandwiched between two members which are to be bonded together in order to minimize the structural failures induced by the bonding and loading characterists of the two members and the method of making such an apparatus.
2. Description of the Prior Art
With the present bonding techniques for bonding materials with different thermal coefficients of expansion and specific adhesion properties, strain related failures caused by thermal expansion mismatches and different adhesive properties between the different materials have been detected during temperature cycling.
For example, when two members are bonded together along their continuous interface, the weaker member will tend to experience a structural failure under a variety of loading conditions which includes thermal loading. This happens, in part, because the weaker member is not able to freely deform in those regions where it is most severly strained. By bonding the two members together at localized regions of traditionally low strain, this situation can be avoided. That is, regions of traditionally high strain are not bonded and are therefore free to deform in such a way as to reduce the strain in these critical areas. High strain regions commonly exist in the corners and at the mid-span locations along the edges of rectangular members. Hence, bonding between members should not occur at these corner or mid-span locations.
Presently, there are various techniques used in the bonding of two disimilar materials together in order to overcome the aforesaid problem. One such technique is selective bonding in which the selected bonding agent or adhesive is applied to preselected areas of one of the members to be bonded. However, this technique normally requires special equipment and additional processes to be implemented and thus proves to be quite expensive. Alternatively, the selective application may be done manually but quality problems inherent in large area bonding due to inconsistent control of the process result. Further, the application of the bonding agent or adhesive to specific areas of members, having dissimilar adhesive properties, to be bonded together may compromise the quality of the bond and result in mechanical failure, due to shock or severe temperatures. The reduction in bonding quality may be primarily attributable to the condition of having equally sized bonding areas on the opposed surfaces of the members with one of the surfaces demonstrating a lower specific adhesion ability than the other surfaces demonstrating a lower specific adhesion ability than the other surface with respect to the selected adhesive.
Another technique to minimize structural related failures is to select thermally matched materials to be bonded together, that is those which demonstrate the same coefficient of thermal expansion and adhesive characteristics. However, such a solution introduces various processing compatibility problems, such as weldability, solderability, plateability, environmental stability, and most importantly an increase in cost.
Another technique uses a flexible adhesive in order to reduce structural failures, but sacrifices both conductivity, if necessary and mechanical age stability.